During many years, micromotors based on electromechanically active materials, such as e.g. piezoelectric materials, have been used for many various applications. In particular in different consumer products, where small volume, low weight, low power consumption and inexpensive arrangements are appreciated, such motors have been used. Such motors are often characterized by a relatively high speed, silent movement, low power consumption, high position accuracy etc. In order to reach very high positioning accuracies, different motion mechanisms such as “walking” mechanisms, stick-slip mechanisms, “inertial” positioning, peristaltic mechanisms or stepping mechanisms have typically been used. In such mechanisms, the motion is based on repetitive operation of a plurality of electromechanically active actuator elements. Walking and stepping mechanisms are typically the most accurate.
Very successful examples of such electromechanical motors are disclosed in the U.S. Pat. No. 6,798,117 and U.S. Pat. No. 7,355,325. Two sets of drive elements are alternatingly contacting an object to be moved. The drive elements are connected to a common back and further attached to a housing of the motor. In order to allow for transferring a motion to the object, the drive elements have to be connected to the housing in such a way that the housing acts as a counterhold for the driving forces in the driving direction. Furthermore, the drive elements have to be hold against the surface of the object to be driven by a certain normal force in order to be able to drive the object. In U.S. Pat. No. 6,798,117, the drive elements are firmly attached to the housing to provide the “stiffness” in the driving direction. The normal force is provided by a spring means acting against a pair of rollers, in turn pushing the object towards the actuators or drive elements.
In order to achieve a well-defined operation, the accuracy of the surfaces has to be very good. Differences in distance and angle between the actuators and the driven object caused by alignment errors, including mounting errors, non-planarity, wear, deformation etc., result in uncertainties of the exact driving conditions. This may influence speed, force and positioning accuracy. The motor stator therefore has to be able to adapt to the various relative alignment errors between the driven object and the support of the stator.
A general problem with prior art electromechanical motors is thus that they are relatively sensitive to the support of the stator.